Which of the following subsets are subspaces of the vector space C(-∞, ∞) and why or why not? V is the set of all real-valued continuous functions defined on R1. If f ang g are in V we define f+g by (f+g)(t) = f(t) + g(t). If f is in V and c is a scalar, we define c . f by (c . f)(t) = cf(t). Then V is a vector space which is denoted by C(-∞, ∞).

a) All nonnegative functions

b) All constant functions

c) All functions f such that f(0) = 0

d) All functions f such that f(0) = 5

e) All differentiable functions

I'm lost on this and does anybody know a good website to learn about subspaces and subsets. My book is not that great. Thanks!